Human renin activation by protease from the renin granule fraction of the dog kidney cortex

Rat renal prorenin concentration in experimental hypertension

The amount of renal prorenin in models of hypertension in rats was studied by using a novel enzyme (PreR-Co). Ten microgrames of PreR-Co promoted a complete conversion of inactive renin, and during the first 15-min incubation the reaction was under initial velocity conditions. The enzyme-substrate reaction obeyed Michaelis-Menten kinetics, with a Vmax of 0.97 x 10(-5) pmol Ang I/min and a Km of 5.03 x 10(-5) pmol prorenin. The difference between the total renin concentration (TRC) and active renin concentration (ARC) in the normal rat kidney (356.4 +/- 20.6 and 105.3 +/- 7.6 ng Ang I/mg tissue/h respectively), indicated that inactive renin comprised 70% of TRC. In the aortic coarctation model, inactive renin comprised 68 % of TRC in the right kidney and no or very little prorenin was found in the left kidney. In the Goldblatt 2-kidney, 1-clip rats, the right kidney prorenin comprised 61% of the TRC and 54% in the clamped left kidney. After DOCA-Salt treatment prorenin was almost absent in the rat kidneys. In conclusion, we have developed an easy and sensitive method to measure inactive renin in the kidney that may be useful to study the biochemical events of renin maturation in physiological and pathological states.

Activation of renal renin by a protein plasma fraction: a novel enzymatic mechanism

A 3-fold increase in active renin was found after a kidney cortex extract was incubated with plasma from either normal or nephrectomized rats (0.34 +/- 0.04 to 1.34 +/- 0.08 and 1.60 +/- 0.06 micrograms Angiotensin I/mg tissue/hr, respectively). A plasma protein that activates renal renin was purified 900-fold. Purification of the protein was achieved by a combination of ammonium sulfate fractionation, molecular filtration on Sephacryl S-200 HR and ion-exchange chromatography on Mono Q HR 5/5 associated to an fast performance liquid chromatography (FPLC) system. The protein shows a molecular weight of approximately 54,000 Da. Renin activation was not inhibited by serine protease inhibitors, such as phenylmethyl sulfonylfluoride, aprotinin, soybean trypsin inhibitor and N-tosyl-L-phenylalanine chloromethyl ketone or by the cystein protease inhibitors N-ethylmaleimide and leupeptin. By using enzyme inhibitors, it was found that the activation process is not mediated by kallikrein, plasmin, tonin, cathepsin B or trypsin-like enzymes. From these results, we conclude that there is in circulating plasma a previously unidentified enzyme capable of activating inactive kidney renin. However, the possibility that this protein acts by activating the renin-substrate reaction cannot be dismissed.

Active and inactive renin in the plasma of the snake bothrops jararaca

1. Complementing the work of Gervitz R. K., Hiraichi E., Fichman M. and Lavras A. A. C. Comp. Biochem. Physiol. 86A, 503-507 (1987), conditions have been established for measuring plasma renin activity (PRA) of the venomous snake Bothrops jararaca (Bj). 2. It corresponded to 115.9 +/- 11.5 ng equivalents of angiotensin II (AII) per ml of plasma (N = 13). 3. PRA did not increase when Bj plasma was submitted to acid-cryo-trypsin Bitis arietans venom activation of inactive renin. 4. This may indicate either absence of inactive renin in this plasma or lack of its activation, due to the already demonstrated (Nahas L., Kamiguti A. S., Betti F., Martins I. S. S. and Rodrigues M. I., Comp. Biochem. Physiol. 69A, 739-743, 1981; Prezoto B. C., Hiraichi E., Abdalla F. M. F. and Picarelli Z. P., Comp. Biochem. Physiol. 99C, 135-139, 1991) absence of factor XII.

Active and inactive renin after exercise

The effects of graded exercise on plasma concentrations of active and inactive renin were studied in seven healthy men. Exercise was performed on a cycle ergometer at four different exercise intensities (corresponding to 30%, 50%, 80% and 87% of VO2max) for 10 min each. Concentrations of active renin and total renin after activation by trypsin were measured by direct immunoradiometric assay. Non-trypsin-activated renin concentration (inactive) was obtained by subtraction. Active renin concentrations at 30%, 50%, 80% and 87% of VO2max were 1.2, 1.9, 3.1 and 4.6 times higher than the control concentration, respectively. Similar increases in plasma renin concentration, determined by conventional enzymatic assay, were observed at every stage. In contrast, changes in inactive renin concentration were not significant at any stage. Significant increases in noradrenaline concentration were found at every exercise stage, but adrenaline, aldosterone and lactate concentrations were significantly elevated only after exercise at 50%, 80% and 87% of VO2max. The similarity between the changes in concentration of active renin and noradrenaline would suggest that sympathetic nerve activity may have been responsible either for the release of active renin or for the conversion of inactive renin to its active form in the kidney.